Emulsions are disperse systems consisting of two or more mutually insoluble or sparingly soluble liquids. The liquid usually present in excess is termed the continuous or external phase, while the liquid dispersed in it is termed the dispersed or internal phase.
If the external phase consists of water, and the internal phase consists of an organic liquid, i.e., mineral oil, the term oil-in-water (O/W) emulsion is used. If water is finely dispersed in a nonaqueous liquid, a water-in-oil (W/O) emulsion is produced. If two nonaqueous liquids are emulsified in each other, the term oil-in-oil (O/O) emulsion is used.
The term three-phase emulsion is used herein to describe a system of three mutually insoluble liquids which are emulsified simultaneously. Technically, it is not what is commonly referred to as a multiple emulsion, in which only two mutually insoluble liquids are present. For example, in the three-phase emulsion of the present invention, an organic oil and water are emulsified into a silicone oil continuous phase, although all three of the liquids are otherwise mutually insoluble one in the other.
While O/W and W/O emulsions containing a silicone oil are common, O/O emulsions in which at least one of the phases is a silicone oil are quite rare. Reference may be had, for example, to the Journal of Colloid and Interface Science, Volume 195, Pages 101-113, Article No. CS975158, Jan. 1, 1997, which describes certain paraffin oil-in-silicone oil O/O emulsions, as well as certain silicone oil-in-paraffin oil O/O emulsions.
Quite unexpectedly, it has now been found that one skilled in the art is enabled to readily prepare silicone oil containing O/O emulsions, as well as three-phase emulsions, using as the emulsifier, an elastomeric silicone polymer according to the present invention. While the elastomeric silicone polymer contains polyether groups which are characteristic of many organic emulsifiers, it is also a three-dimensional molecular polymeric network consisting of tens, hundreds, and even thousands of crosslinking units between and among its polymeric molecules, and therefore one would not normally expected it to function as an emulsifier in a nonaqueous system such as an O/O emulsion. It is also unexpected that a single emulsifier could be used to form both O/O emulsions and three-phase emulsions.
In comparison to silicone polyether emulsifiers, i.e., glycol modified siloxanes, which are not crosslinked molecules, an additional unexpected benefit of using a crosslinked elastomeric silicone polymer as emulsifier for three-phase emulsions, is that it is capable of thickening the external silicone oil phase of the emulsion. This eliminates the need of separate thickening agents in order to achieve the desired viscosity of the final emulsion. It also eliminates the need of using high internal phases, i.e., where the amount of internal phase exceeds the amount of external phase, to achieve the same result as in WO 97/17938 (May 22, 1997), for example.